This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to the prior art by inclusion in this section.
In telecommunication system, an access node or access point facilitates wireless communication between a terminal device, such as user equipment (UE), with a core network. An access node is also referred to as radio base station (RBS), node B (in 3G Networks), base transceiver station (BTS), evolved Node B (eNB) or, base station (BS). It mainly consists of three basic portions, a baseband unit, a radio unit and an antenna unit. The baseband unit is used for baseband signal processing such as modulation/demodulation, encoding/decoding, pre-coding, channel estimation and equalization, etc. The radio unit is used for frequency conversion to high band (Downlink) or to lower band (Uplink), output power amplification is also implemented in radio unit. Antenna unit comprising antenna elements is to transmit and receive radio frequency (RF) signal through air interface.
In a traditional macro configuration, baseband unit is physically bound to radio unit. In real deployment, both of the baseband unit and the radio unit are put together in a cabinet (102) as shown in FIG. 1 on the ground, while antenna unit (101) is always horizontally higher than the radio unit, usually located at the top of buildings in the city or on the mountains in countryside, to ensure the transmission and reception of electromagnetic waves. Long jumper cable is used to connect the radio unit and the antenna unit (101) in FIG. 1.
Along with development of technology, main-remote concept was raised during the evolution of access node. Radio unit (202) is not necessarily close to baseband unit (203) but installed considerably close to antenna unit (201), shown in FIG. 2. However, connection between antenna unit (201) and radio unit (202) still relies on jumper cable.
In recent years, antenna integrated radio unit (AIR) was designed to put radio unit and antenna unit into one physical “box” (301) as shown in FIG. 3. Long cable is needed between the physical box (301) and baseband unit (302). When a concept of Multiple In and Multiple Out (MIMO) became popular, number of antenna element has been increased from one or two to eight or even 16. On the other hand, antenna technology development turned it into reality that antenna element can be made into planar antenna element and be patched onto an antenna layer.
FIG. 4 illustrates how a radio unit and an antenna unit are connected in a same physical block of an AIR model. Radio Unit (401) includes a multi-layer Printed Circuit Board (PCB) with several radio components mounted on one side of the radio PCB. Antenna Unit (403) includes an antenna PCB and several antenna elements patched on one side of the antenna PCB. A Filter Unit (402) is between the radio PCB and antenna PCB to filter out unnecessary interference outside required spectrum. Each side of the filter unit is connected to the other side of the radio PCB and the antenna PCB respectively. Signals transmitted between the radio unit and antenna unit go through the wired connection.
In the above mentioned MIMO system, a plurality of antenna elements are designed to transmit signals through a plurality of radio branches. Assuming N radio branches are designed, there are N connectors between a filter unit and an antenna unit, and N connectors between the filter unit and a radio unit. The larger the N is, the more connectors are needed. Not only the cost of the connectors is rather high, but the difficulty of assembling the 2N connectors is considerable especially N increases to 64 which is popular in the 4th generation (4G) telecommunication system.